Flow rate and duty cycle effects in lysis of Chlamydomonas reinhardtii using high-energy pulsed focused ultrasound

Abstract

To consider microalgae lipid biofuel as a viable energy source, it is a necessity to maximize algal cell lysis, lipid harvest, and thus biofuel production versus the energy used to lyse the cells. Previous techniques have been to use energy consumptive ultrasound waves in the 10-40 kHz range in a stationary exposure environment. This study evaluated the potential of using 1.1 MHz ultrasound pulses in a new flow through type chamber on Chlamydomonas reinhardtii as a model organism for cell breakage. The ultrasound was generated using a spherically focused transducer with a focal length of 6.34 cm and an active diameter of 6.36 cm driven by 20 cycle sine-wave tone bursts at varied pulse repetition frequencies. First, variations in flow rate were examined at a constant duty cycle of 3.6%. After assessing flow rates, the duty cycle was varied to further explore the dependence on the tone burst parameters. Cell lysis was assessed by quantifying protein and chlorophyll release into the supernatant as well as by lipid extractability. Appropriate flow rates with higher duty cycles led to statistically significant increases in cell lysis relative to controls and other exposure conditions. KeywordsGenetics Development and Cell Biology, Food Science and Human Nutrition, biofuels, cells, cytology, ultrasonics, biofuel production, chlamydomonas reinhardtii, exposure conditions, focused transducer, focused ultrasound, high-energy pulsed, pulse repetition frequencies, flow rate Flow rate and duty cycle effects in lysis of Chlamydomonas reinhardtii using high-energy pulsed focused ultrasound To consider microalgae lipid biofuel as a viable energy source, it is a necessity to maximize algal cell lysis, lipid harvest, and thus biofuel production versus the energy used to lyse the cells. Previous techniques have been to use energy consumptive ultrasound waves in the 10-40 kHz range in a stationary exposure environment. This study evaluated the potential of using 1.1 MHz ultrasound pulses in a new flow through type chamber on Chlamydomonas reinhardtii as a model organism for cell breakage. The ultrasound was generated using a spherically focused transducer with a focal length of 6.34 cm and an active diameter of 6.36 cm driven by 20 cycle sine-wave tone bursts at varied pulse repetition frequencies. First, variations in flow rate were examined at a constant duty cycle of 3.6%. After assessing flow rates, the duty cycle was varied to further explore the dependence on the tone burst parameters. Cell lysis was assessed by quantifying protein and chlorophyll release into the supernatant as well as by lipid extractability. Appropriate flow rates with higher duty cycles led to statistically significant increases in cell lysis relative to controls and other exposure conditions.

Histotripsy Treatment of <italic>S. Aureus</italic> Biofilms on Surgical Mesh Samples Under Varying Scan Parameters

“…The clear reduction in CFUs relative to the sham at these higher exposure levels shows that the bacteria in the vicinity of the mesh are being killed by the ultrasound histotripsy at least at the higher levels. This is in agreement with our earlier studies which showed a fragmentation of microalgae following histotripsy level exposures [34, 35]. The fate of the bacteria on the mesh at the lower exposure levels is still not certain due to the enormous number of bacteria spontaneously released by the biofilm as is evidenced by the large number of CFUs on the gel for the sham exposures.…”

“…This liquefied chamber could potentially allow for the formation of strong streaming currents and associated shearing forces on the bacteria when the focal zone passes through the treatment zone on subsequent passes as the focal zone was passed over the mesh 5 times. In our earlier studies with microalgae [34, 35], it is clear that the fragmentation of micro-organisms his greatly enhanced when fluid streaming is present. However, the creation of these liquefied pockets is likely not desirable in general as they would greatly increase the collateral damage to healthy surrounding tissue.…”

Histotripsy Treatment of S. Aureus Biofilms on Surgical Mesh Samples Under Varying Pulse Durations

“…Hence, we may be releasing the bacteria from the biofilm without killing them. This possibility is doubtful given the fragmentation of microalgae that was observed in some of our earlier studies [52, 53], but we cannot make the claim of bacteria killing from this study. Instead, all we can conclusively say is that the biofilms have been disrupted by our therapy while our hypothesis continues to be that the bacteria are destroyed and not just released.…”